The present invention relates to high speed synchronous communication networks and more particularly to a system and method for detecting a failure on one or more among N physically separate telecommunication lines and then for automatically re-adjusting the available user bandwidth to efficiently utilize the remaining operational telecommunication lines.
The present communication carrier networks have evolved over time from data transmission using mostly analog techniques into entirely digital networks. New industry standards for the transmission and the reception of data have emerged including among other things, methods for channelization, data multiplexing and demultiplexing, switching and cross-connection routing of data from one user to another . . . . The CCITT standards specify data signal voltage levels and template characteristics, framing formats, clocking and signal jitter characteristics. They allow the different manufacturers to connect their equipment to the carrier networks and to inter-operate with each other. In the United States, said standards have been, in particular, the object of a large number of patents relative to clock recovery, alignment and synchronization within a single channel:
U.S. Pat. No. 4,394,758, xe2x80x9cTiming circuits for PCM receptionxe2x80x9dxe2x80x94Donne et al.
U.S. Pat. No. 4,394,759, xe2x80x9cDigital information transmission systemxe2x80x9dxe2x80x94Donne et al.
U.S. Pat. No. 4,417,348, xe2x80x9cDigital channel protection switching for radio communicationsxe2x80x9dxe2x80x94Abbruscato et al.
U.S. Pat. No. 4,458,356, xe2x80x9cCarrier wave restoration circuit for receiverxe2x80x9dxe2x80x94Toy et al.
U.S. Pat. No. 4,630,286, xe2x80x9cMultiple telephone circuit synchroniser for high speed dataxe2x80x9dxe2x80x94Betts et al.
U.S. Pat. No. 4,675,886, xe2x80x9cFrame synchronising unit with word-locking decoderxe2x80x9dxe2x80x94Surie et al.
U.S. Pat. No. 4,734,920, xe2x80x9cHigh speed modem for multiple communicationxe2x80x9dxe2x80x94Betts et al.
U.S. Pat. No. 4,744,095, xe2x80x9cDiversity channel switch with automatic data rephasingxe2x80x9dxe2x80x94Cornet et al.
U.S. Pat. No. 4,775,987, xe2x80x9cTransmitter for high bit rate data over telephone systemxe2x80x9dxe2x80x94Miller et al.
U.S. Pat. No. 4,818,995, xe2x80x9cParallel transmission system using step as line coding typexe2x80x9dxe2x80x94Takasaki et al.
Standardization, while useful, is sometimes not cost effective because the granularity of bandwidth to the user does not always meet his needs. The user must reserve bandwidth in the increments tariffed by the individual countries. If a higher bandwidth is required than provided by a given type of channel, the user is forced to buy the next higher increment of bandwidth even though the tariffed bandwidth far exceeds his requirement. For example, in Europe, a user requiring more than the E1 bandwidth of 2 Mbps is forced to buy E3 bandwidth of 34 Mbps. A user in the US requiring more than T1 bandwidth of 1.544 Mbps is forced to buy T3 bandwidth of 44.736 Mbps.
Other patents in the field of interest deal with combining a number of low speed transmission lines to provide a higher bandwidth to the user without the need to xe2x80x9cjumpxe2x80x9d to the next tariffed level of bandwidth service.
U.S. Pat. No. 5,251,210 entitled xe2x80x9cMethod and Apparatus for Transforming Low Bandwidth Telecommunications Channels into a High Bandwidth Telecommunications Channelxe2x80x9dxe2x80x94Mann et al discloses a method and system for combining lower bandwidth channels to produce a higher bandwidth channel.
European patent application 96480090.8 (U.S. patent application Ser. No. 807496) entitled xe2x80x9cSystem and Method for creating N-times E1/J1 bandwidth from N separate physical E1/T1 linesxe2x80x9dxe2x80x94Poiraud et alxe2x80x94describes a system and method for aggregating data on multiple physically separate lower-speed E1/J1 channels to generate a higher bandwidth. The high speed data stream is first divided into lower bandwidth channels and then transmitted through the network. The previously divided data stream arrives with varying delays depending on the physical characteristics of the network. Low bandwidth channels are aggregated together into a high bandwidth channel by determining the different geographical delay parameters among the lower speed channels, adjusting the transmission delays by alignment circuitry, and then combining the lower speed signals into one high bandwidth channel for the user. The method for the delay adjustment consists in adding a pseudo-random noise pattern to each of the lower bandwidth channels, measuring the time difference among all the channels, and then adjusting the time differences in the received data stream so that the combination of the signals produces a coherent higher bandwidth data stream. This application is an improvement of U.S. Pat. No. 5,521,210 adapted to the European telecommunication environment.
However, the field of these patents is limited in scope because they do not disclose any error recovery or bandwidth adjustment mechanism in case one of the lower bandwidth channels becomes inoperative.
It is therefore the object of the present invention to provide a method and system for detecting a failure on one or more among N physically separate telecommunication lines and then for automatically re-adjusting the available user bandwidth to efficiently utilize the remaining operational telecommunication lines. It is also the purpose of this invention to allow the user to buy a service using N+1 physical lines and to use N physical lines for normal data transmission with the possibility to replace a failing line with the spare line if one line becomes unusable.
When a high bandwidth data stream, multiple of lower bandwidth channels, is separated into N separate physical data streams according to the method claimed in the aforementioned U.S. Pat. No. 5,251,210 and European Patent application 96480090.8 (U.S. patent application Ser. No. 807496) data are transmitted over different physical paths and are received with different delays among the N physical lines. The aforementioned inventions take into account the different delay characteristics of the different physical lines. The object of the present invention is to continuously detect line status and adjust the bandwidth so as to provide the maximum bandwidth available if one of the physical lines becomes unusable and also to detect and adjust the bandwidth if the previously unusable line becomes usable once again.
The alignment of lower bandwidth data into a higher bandwidth operates by using some of the bandwidth of each lower bandwidth channel as a common timing signal. Each lower bandwidth signal is transmitted to the network with identical timing information. At the destination, the timing information is recovered for each signal independently and is used to recombine the low bandwidth signals into a single high bandwidth signal. The term for this process is to cohere the output from the network into a high bandwidth signal. This process is briefly described below since knowledge of this technique is necessary for understanding how to detect and adjust bandwidth when one of the physical lines becomes unusable.
The timing information is a xe2x80x9csuperframexe2x80x9d signal added into one bit position of each lower bandwidth channel frame. The effective bit rate of each constituent link is thus reduced, but not significantly. For example, the bit rate of N cohered E1 links is Nxc3x971976 kbps versus the available bandwidth of 1984 kbps. The T1 or J1 bit rate is reduced to 1536 kbps from 1544 kbps. The xe2x80x9csuperframexe2x80x9d signal is a pseudo-random noise sequence from a shift register generator. The auto-correlation properties of pseudo-random noise sequences make them ideal for such timing purposes.
At the source, the same bit of the pseudo-random noise sequence is inserted on each line. These pseudo-random noise sequences inserted on each transmission line are used at the destination to align the data received from the network. At the destination, pseudo-random noise sequence receivers independently acquire the phase of the timing information in each physically separate signal. However, since separate physical paths are used for the transmission of the data, the data at the receiving end is not in the same data-bit sequence as the data that was transmitted at the source. These differential delays between the physical channels can be resolved by using the difference in superframe phases. This function can be accomplished because the transmitting end inserted the receive alignment signals in the same bit position relative to the superframe signals in the data stream (Superframe signals are used by the network to ensure that all user data remains in the same relative time position to a common reference point i.e. the superframe signal.). The process of determining the relative time position of user data to a common reference point and then compensating for this time difference is called coherence throughout in this application. Based on the measured time differences between the superframe signal and the pseudo-random noise bit in the data stream, the relative delay across all the channels can be determined. This delay variance is then compensated for and the low bandwidth channels combined to receive data effectively as a single high bandwidth channel.
When one or more of the physically separate lines becomes inoperative, the transmitted data is no longer received on the inoperative line and the entire data stream cannot be reassembled correctly. Therefore, the whole bandwidth is lost even though Nxe2x88x921 of the physically separate lines are still usable. This impacts the cost of the lines plus the time the user is without any form of data transmission.
The present invention discloses a technique for detecting a failure on one or more among a N physical lines and for automatically compensating for this loss by using the available bandwidth of the remaining Nxe2x88x921 operational lines. This is accomplished by specific detection and automatic realignment functions. When a receiving end framer in one of the multiplexers at both ends of the physical lines has detected a loss of alignment, high error rates or the loss of a physical line, the bandwidth is automatically re-adjusted with the remaining lines. When conditions on a line are marginal e.g. high error rates, a communication protocol between the transmitting and receiving ends of a line determines if the error rate is too high for the required service and, thereby triggers the automatic adjustment of the bandwidth to Nxe2x88x921 times the number of available lines. When the channel is restored to an acceptable level of service, the communication protocol automatically re-adjusts the bandwidth to the full N channels. When the network indicates the loss of a line, the multiplexers at both ends of the link automatically compensate for the loss without any message exchange. When the line is restored, the multiplexers at both ends of the link automatically re-adjust the bandwidth.
More particularly, the present invention relates to a method and system for readjusting bandwidth in case of failure on one or more among a plurality of low bandwidth channels in a system in a communication network for disassembling a relatively high bandwidth datastream into a plurality of relatively low bandwidth datastreams each having a plurality of data frames, which are transmitted on said corresponding plurality of relatively low bandwidth channels, said disassembling system carrying out the steps of:
dividing said high bandwidth datastream into a plurality of relatively low bandwidth datastreams each having a plurality of data frames;
concurrently inserting an alignment signal into each corresponding data frame of each of said relatively low bandwidth datastreams; the consecutive alignment signals in data frames of each of said relatively low bandwidth datastreams constituting a pre-determined alignment pattern;
concurrently transmitting a respective one of said low bandwidth datastreams including the concurrently inserted alignment signal on a respective one of said relatively low bandwidth channels;
said method comprising the steps of:
detecting a failure on one or more among the plurality of relatively low bandwidth channels;
inserting a failure signal in the data frames of the relatively low bandwidth datastream corresponding to the failing low bandwidth channel, consecutive failure signals constituting a predetermined failure bit pattern recognizable by a system for assembling a relatively high bandwidth datastream from a plurality of relatively low bandwidth datastreams;
replacing in the data frames of the relatively low bandwidth datastream corresponding to the failing low bandwidth channel the alignment signal by a failure signal, consecutive failure signals constituting a predetermined failure bit pattern; recognizable by a far end system for assembling a relatively high bandwidth datastream from a plurality of relatively low bandwidth datastreams;
transmitting the relatively low bandwidth datastream corresponding to the failing low bandwidth channel with the inserted failure pattern; and
dividing and transmitting the high bandwidth datastream over the remaining available low bandwidth channels.